A widely used carbamate herbicide, CIPC, can impair growth, modify cell shape, perturb the microfilament system and cause the disappearance of microtubules in mouse 3T3 fibroblasts. Withdrawal of CIPC after 5-7 days of culture leads to recovery of cell growth and shape within 2-3 days, associated with a partial recovery of the cytoplasmic microtubule and microfilament systems. However, nuclear division is highly abnormal in such "recovering" cells: they develop multipolar spindles during mitosis and a high proportion of interphase cells contain multiple, often multilobed nuclei. In addition at cytokinesis nuclei are often not partitioned between the daughter cells. The basis of these abnormalities of mitosis and cytokinesis will be further explored by use of two fluorescence dyes, Hoechst 33258 and DAPI. These substances bind DNA and enable visualization of chromosome movement during mitosis in living cells as well as fluorometric measurement of quantities of DNA in interphase nuclei. We will continue to seek the precise interaction of CIPC with proteins of the microtubule or microfilament systems by in vitro study of purified proteins. In particular the interaction of CIPC with high molecular weight proteins that copurify with tubulin and actin will be examined.